Events and actions

See the rustdoc for Event and Action for the full definitions.

Action ordering

step() returns Vec<Action<C>> in causal order. Every action that must reach stable storage before any subsequent network send appears earlier in the vector. Hosts must:

• Process actions in order.
• Flush PersistHardState / PersistLogEntries / PersistSnapshot to disk before performing any Send that follows them.

This is Figure 2’s “respond to RPCs only after updating stable storage”. The engine enforces it on the host side of the contract.

Actions that don’t need fsync

• Send { .. } — best-effort. The engine retries on its own cadence.
• Apply(entries) — feed to the state machine. The engine advances last_applied when emitting this; the host must not skip it.
• ApplySnapshot { bytes } — restore the state machine.
• Redirect { leader_hint } — fail the user’s pending reply with NotLeader.
• SnapshotHint { .. } — advisory. Ignore, debounce, or act.
• ReadReady { id } — the read with this id is now safe to serve.
• ReadFailed { id, reason } — surface the reason to the caller.